Abstract. Daily PM10 samples were collected at two urban sites within two valleys
in the French Alps (Chamonix and St Jean de Maurienne) during a period of
two and a half years. The carbonaceous species EC (elemental carbon) and OC
(organic carbon) were analysed to investigate the possible sources of EC and
OC, and their seasonal variations. Mean OC concentrations are in the very
high range of concentrations measured for other European sites, and
represent at least one third of the PM10 mass on each site. On the
basis of the comparison between EC and OC concentrations with several
tracers, we were able to show that their main sources are local primary
combustion sources. Biomass burning emissions (residential heating) have a
significant impact on OC concentrations while heavy duty traffic emissions
have an impact only on EC concentrations. Finally, we estimated the
contribution of SOA (secondary organic carbon) to OC, using the EC-to-OC
primary ratio method (Castro et al., 1999) and demonstrated that the
calculation of SOA mass with this method is highly uncertain, if the
hypothesis of a constant primary EC-to-OC ratio is not very closely
examined.